Why cloud coverage is not available in yesterday and history functions?

thank you for this very well documented API. It's really a pleasure to use it. I'm monitoring some parameters trhough the hourly function including 'cloud_coverage' and I would like to validate it through the observations done and available in yesterday function. But the nearest match is 'conditions' which is not pertinent to monitor it.
Is it possible to access hourly cloud coverage observations in another manner?